﻿namespace DigitalThermometer.OneWire
{
    internal static class Crc8Helper
    {
        private static readonly byte[] Crc8Table =
        {
            0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65,
            157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220,
            35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93,  3, 128, 222, 60, 98,
            190, 224,  2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255,
            70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89,  7,
            219, 133, 103, 57, 186, 228,  6, 88, 25, 71, 165, 251, 120, 38, 196, 154,
            101, 59, 217, 135,  4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36,
            248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91,  5, 231, 185,
            140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205,
            17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80,
            175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238,
            50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115,
            202, 148, 118, 40, 171, 245, 23, 73,  8, 86, 180, 234, 105, 55, 213, 139,
            87,  9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22,
            233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168,
            116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53
        };

        /// <summary>
        /// Calculate CRC8 checksum of given byte array
        /// </summary>
        /// <param name="array">Array</param>
        /// <returns>Value of CRC8 checksum</returns>
        internal static byte CalculateCrc8(this byte[] array)
        {
            if (array is null) throw new ArgumentNullException(nameof(array));

            return CalculateCrc8(array, 0, array.Length - 1);
        }

        /// <summary>
        /// Calculate CRC8 checksum of given byte array
        /// </summary>
        /// <param name="array">Array</param>
        /// <param name="startIndex">Start index</param>
        /// <param name="endIndex">EndIndex (inclusive)</param>
        /// <returns>Value of CRC8 checksum</returns>
        internal static byte CalculateCrc8(this byte[] array, int startIndex, int endIndex)
        {
            if (array is null) throw new ArgumentNullException(nameof(array));

            byte crc8 = 0x00;

            for (var i = startIndex; i <= endIndex; i++)
            {
                crc8 = Crc8Table[crc8 ^ array[i]];
            }

            return crc8;
        }
    }
}